Mesogenic biphenyl benzoates

ABSTRACT

The present invention relates to a family of substances which, in different temperature ranges, exhibit smectic or nematic properties of mesomorphism. Their general formula is: ##STR1## where R designates one of the three radicals: 
     
         C.sub.n H.sub.2n + 1 ; 
    
      ##STR2## (n being a whole number ranging from 1 to 20) and X designatating a halogen (Br preferably) or the nitrile radical C N.

The present invention relates to mesogenic products comprising asubstance or a mixture of substances which, within a certain temperaturerange, exhibit a mesomorphic phase, characteristic of liquid crystal.

The possible applications in display cells, of various liquid crystals,depends upon the nature of their mesomorphism (nematic or smectic inparticular), the extent of their temperature range, and differentfactors such as dielectric anisotropy, coloration and stability.

The mesogenic products in accordance with the invention are stable,colorless, and have a positive dielectric anisotropy in excess of 5. Bymixing it is possible to widen and narrow the temperature rangeexhibited by the substances in the pure state.

According to the invention, there is provided mesogenic products of thegeneral formula: ##STR3## wherein R belongs to the group of thefollowing three radicals:

    C.sub.n H.sub.2n + 1 - .spsb. ##STR4## where n is a whole number ranging between 1 and 20; and wherein X belongs to the following group : a halogen and the nitrile radical (C N).

A method of manufacturing those products is as follows.

First case : X = Br or Cl

A parabenzophenol ester of the formula : ##STR5## where R is one of theaforesaid radicals, is bromated (or chlorinated). An ester of this kinditself has been previously obtained in a manner known per se for exampleby reacting organic acid chloride containing the radical, withparabenzophenol.

In the case of bromide, the parabenzophenol ester reacts at ambienttemperature when liquid bromide is poured into a solution of ester andacetic acid. The bromating efficiency is of the order of 50% and yieldsa compound of the formula: ##STR6## Second case : X = C N

In a first stage, the operation described in in the first case isperformed, yielding the compound formula (3).

In a second stage, the bromide is replaced by the nitrile group in thecompound of formula (3). For this purpose, the latter is reacted at 200°C. with cuprous cyanide in the liquid phase (dimethyl formamide).

Example of the first case : X = Br and R = C₈ H₁₇

Using a known method, a quantity of parabenzophenol nonanoate isprepared : ##STR7## representing 0.06 mols, this being dissolved in amixture containing 32 milliliters of acetic acid and 16 milliliters ofacetic anhydride, in which a small iodine crystal (for example one tenthof a gram) has previously been dissolved. Then at 35° C., a quantity ofbromide representing 0.18 mols is poured slowly in. The reaction isallowed to take place for twelve hours at ambient temperature. Theprecipitate form is filtered off, rinsed in acetic acid and then water.The liquors are concentrated by evaporation using heating, and thenrefiltered. The precipitates are filtered and recrystallised in ethanol.In this way, 0.35 mols of p'-benzophenol-p-bromononanoate are obtained.

Example of the second case : X = C N and R = C₈ H₁₇

Using the method described in the previous example, a certain quantityof p'-benzophenol-p-bromo-nonanoate is prepared, 0.025 mols of which aredissolved in a solution containing 0.03 mols of cuprous cyanide in 14milliliters of dimethylforamide. The reaction is allowed to take placeat 200° C. for six hours. Following this, the solution is poured into amixture containing 25% of ethylene diamine and 75% of water. The productis extracted using ether and then purified by a chromatographictechnique on a silica column. The result is 0.008 molsofp'-benzophenol-p-nitrile nonanoate.

The following table sets out the mesomorphism observed in respect of anumber of substances specified by the radical X and the radical Rcontained in the general formula (1) :

    ______________________________________                                        Radical X                                                                             Radical R    Mesomorphism observed                                    ______________________________________                                        Br                                                                                     ##STR8##                                                             smectic from 148° C to 230° C                                   Br                                                                                     ##STR9##                                                             smectic from 133° C to 194° C - nematic from 194° C      to 200° C                                                              Br      C.sub.8 H.sub.17                                                      smectic from 65° C to 100° C                                    CN                                                                                     ##STR10##                                                            nematic from 95.5° C to 230° C (dielectric anisotropy : +8)     CN                                                                                     ##STR11##                                                            nematic from 120° C to 270° C (dielectric anisotropy : +8)      CN      C.sub.5 H.sub.11                                                      nematic from 56° C to 72° C                                                          (dielectric anisotropy : +10)                            CN      C.sub.7 H.sub.15                                                      nematic by supercooling                                                                            below 78°  C                                                           (dielectric anisotropy : +10)                            CN      C.sub.8 H.sub.17                                                      smectic from 26° or 43.5°                                                            to 58° C                                          nematic from 58° C to 76° C                                     ______________________________________                                    

Mixtures of the different substances of formula (1), either between oneanother or with other liquid crystals, make it possible to vary themesomorphic range.

By way of example, take the following substances : ##STR12## in respectof which the following results have been observed :

    ______________________________________                                        Composition of the mixture                                                    (in fractions of mols)                                                                          Observed mesomorphism                                       ______________________________________                                        1/3 A + 1/3 B + 1/3 C                                                                           nematic from 24° to 94° C                     1/2 A + 1/2 B     nematic from 38° C to 111° C                  1/2 C + 1/2 D     smectic (A) from 12° C to                                              46° C, nematic from 46° C to                                    53° C.                                               ______________________________________                                    

What we claim is:
 1. A mesogenic compound of the formula: ##STR13##wherein R is selected from the group consisting of ##STR14## and n is awhole number from 1 to
 20. 2. A mesogenic compound of the formula:##STR15## wherein R is selected from the group consisting of ##STR16##and n is a whole number from 1 to
 20. 3. The mesogenic compound of claim1 wherein R is ##STR17##